The demand for lightweight, powerful lithium-ion batteries as a power supply for vehicles as well as for personal computers and portable terminals (PDAs) is expected to increase greatly in the future. A typical structure of a lithium-ion battery features positive and negative electrodes comprising an active material capable of storing and releasing lithium-ions, a separator positioned between the electrodes, and a nonaqueous electrolyte. For example, a lithium-ion battery is known having a configuration in which an electrode assembly obtained by superposing positive and negative electrode sheets, each having a layer of active material as the main component thereof (active material layer) on the surface of a long continuous sheet collector, and winding the same in the lengthwise direction with a separator interposed therebetween (wound electrode assembly) is housed in a container together with a nonaqueous electrolyte.
Providing a porous layer having an inorganic material as the main component thereof on the electrode surface in a lithium-ion battery of such a configuration can be an effective technique for increasing the reliability (capability of preventing internal shorts, etc.) of that battery. In relation to this type of lithium-ion battery, patent document 1 discloses that the duration of charge retention under high temperature conductions can be extended by providing a porous film of a specified thickness and porosity on the surface of the negative electrode. Patent documents 2 to 4 can be noted as other technical documents relating to lithium-ion batteries.
Patent document 1: Japanese Patent Application Laid-open No. 2006-228544
Patent document 2: Japanese Patent Application Laid-open No. 2008-103310
Patent document 3: Japanese Patent Application Laid-open No. 2003-208891
Patent document 4: Japanese Patent Application Laid-open No. H11-102730